Developmental Biology among Corbiculate Bees: Bombus impatiens, Including Observations on Its Egg Eclosion

Jerome G Rozen,Eli S Wyman,Sarah Kocher,Corey Shepard Smith

doi:10.1206/3912.1

Abstract

This contribution results from an investigation of four commercially obtained colonies of Bombus (Pyrobombus) impatiens Cresson in an attempt to understand the functional anatomy and behavior of its immature stages. Eggs are described in detail, and their chorionic microstructure is contrasted with that of Bombus (Cullumanobombus) griseocollis (De Geer). They are deposited in groups consisting of a few to more than nine eggs into a single chamber. The study confirms that larvae pass through four instars. Although increasing in size dramatically from one instar to the next, larval anatomy and behavior change little during the first three instars. The last instar is the one that commences defecation and production of silk resulting in cocoon construction. In contrast to most bees, its larval activities result in substantial changes in size and shape of its brood chamber, whereas brood chambers of most bees are constructed by the female and modified little by the offspring. This study is a part of a series of investigations into the similarities and differences in the developmental biologies among corbiculate bees.

Highlights

Michener (1953) presented a detailed comparative account of available mature larvae of bees and followed that study with a similar but less complete investigation of pupal bees (Michener, 1954)
J.G.R. has reported on euglossine bees (Garofalo and Rozen, 2001; Rozen, 2016a; Rozen, 2018), his focus has been primarily on the immature stages of noncorbiculate solitary and cleptoparasitic bees, in part because their biologies were understudied relative to those of social bees and in part because his geographic location was removed from areas with a fauna of stingless bees
We present new insights into the nesting biology of this species based on observations of its nests and information concerning immature stages

Summary

INTRODUCTION

Michener (1953) presented a detailed comparative account of available mature larvae of bees and followed that study with a similar but less complete investigation of pupal bees (Michener, 1954). Cnaani et al (2002) presented certain important details of the developmental biology of B. impatiens, but that study was undertaken before SEM investigations were widely available. It did not deal with the subject of egg eclosion, which, as shown below, may be a future fruitful path of inquiry. Because the path was the same as the chorionic split occurring as the first instar started to emerge, there was no doubt that the spicules are involved with the renting of the chorion and were termed “hatching spines.” These have been identified in many groups of bees: see Rozen et al, 2017: table 1. As revealed in this current study, no such double row of spines have been discovered in the case of B. impatiens, but as shown below, there are spines radiating around each of the first instar’s spiracles that do have a function that will almost certainly be found to be involved with ecdysis

MATERIAL AND METHODS

DISCUSSION AND CONCLUSIONS